1. Field of Invention
The invention relates to a projection display apparatus which separates light beams from a light source into red, blue and green light beams. The display apparatus modulates the red, blue and green light beams through light valves provided in a liquid crystal panel in response to image information. The modulated red, blue and green light beams are combined and expansively projected through a projection lens on a projection screen. In particular, the invention relates to a cooling system for efficiently and cleanly cooling the components of a projection display device that separates, modulates combines and projects light beams.
2. Description of Related Art
Conventional projection display devices include an optical unit which optically treats light beams emitted from a light source lamp unit to synthesize a color image in response to image information. The synthesized light beams are projected on a screen through the use of a projection lens unit, a power unit, and a circuit board unit including control circuits and similar devices.
The optical unit separates light beams emitted from the light source lamp unit into red, blue and green color light beams. The optical unit modulates these color light beams with light valves provided in a liquid crystal panel in response to image information. The modulated color light beams are recombined with a cross dichroic prism or similar devices, and are projected on a screen.
Japanese Patent Publication No. 7-225379 discloses a projection display apparatus provided with a polarized light conversion device for aligning the polarization direction of light beams emitted from a light source lamp unit. The polarized light conversion device has a polarized beam splitter array provided with a plurality of sets of polarized light separating films and reflection films which are parallel to each other. The polarized beam splitter array separates incident light beams into two types of straight polarized light components, and aligns the polarization direction of these two types of straight polarized light components.
Some elements of the projection display apparatus, e.g. the polarized light conversion device and the optical unit, are stored in an outer case. A projection side of the projection lens unit is disposed in the outer case such that it protrudes from the front face of the outer case. The outer case is provided with an operating section including a power switch, a light-receiving window for remote control, and an input/output terminal group for sending and receiving signals to and from external devices.
Conventional projection display devices include optical devices in the light source lamp unit, a power unit and an optical unit, all of which are sources of heat. The liquid crystal light valves and their respective polarization plates are major heat sources because they absorb part of the transmitted light beams.
In order to cool the heat sources, the projection display apparatus is provided with a cooling system.
The cooling system introduces fresh air into the outer case through an intake port by a suction fan. The introduced air is circulated through the outer case and exhausted through an air outlet provided on the outer case by an exhaust fan.
In such a cooling system, the power unit, which often become very hot, is provided with a suction fan to introduce the air in the outer case to the interior of the power unit for cooling.
The power unit includes a primary active filter, a power supply, and a ballast. A transmitter FET may be mounted on the circuit board of the primary active filter. A rectifier diode bridge, an oscillating transistor for a D/D converter and a triode regulator for a D/D converter may be mounted on the circuit board of the power supply. Also, devices such as a driving FET for a chopper circuit and a reverse-current preventing diode for a chopper circuit may be mounted on the circuit board of the ballast. Because these devices are heat sources, heat sinks are fixed to them to enhance cooling efficiency. Air introduced with the suction fan cools the heat sinks.
By the time that air is introduced to the power unit in the outer case, it has already been heated by many other elements located in the outer case. Thus, the air introduced to the power unit is hotter than the fresh air introduced into the outer case, and is less efficient in cooling the power unit.
Also, when the air in the outer case is drawn with the suction fan, fresh air containing dust may be introduced through openings of the outer case, e.g., the gap between the projection lens unit and the outer case. As a result, dust may adhere to the optical system and deteriorate the display quality, which reduces the reliability of the apparatus.
The polarized light conversion device is heated because the polarized light separating film and the reflection film absorb some of the incident light. The device has no separate cooling means even though it must be cooled. The polarized light conversion device is therefore cooled by the air circulating from the suction fan to the outlet. Thus, the device may not be efficiently cooled due to insufficient circulation of the cooling air in some apparatus configurations.